Kurapothula Pawan K J, Shepherd Sam, Wilkins David M
Atomistic Simulation Centre, School of Mathematics and Physics, Queen's University Belfast, Belfast BT7 1NN, Northern Ireland, United Kingdom.
J Chem Phys. 2022 Feb 28;156(8):084702. doi: 10.1063/5.0083075.
Hydrogen bonds are of paramount importance in the chemistry of clays, mediating the interaction between the clay surface and water, and for some materials between separate layers. It is well-established that the accuracy of a computational model for clays depends on the level of theory at which the electronic structure is treated. However, for hydrogen-bonded systems, the motion of light H nuclei on the electronic potential energy surface is often affected by quantum delocalization. Using path integral molecular dynamics, we show that nuclear quantum effects lead to a relatively small change in the structure of clays, but one that is comparable to the variation incurred by treating the clay at different levels of electronic structure theory. Accounting for quantum effects weakens the hydrogen bonds in clays, with H-bonds between different layers of the clay affected more than those within the same layer; this is ascribed to the fact that the confinement of an H atom inside a layer is independent of its participation in hydrogen-bonding. More importantly, the weakening of hydrogen bonds by nuclear quantum effects causes changes in the vibrational spectra of these systems, significantly shifting the O-H stretching peaks and meaning that in order to fully understand these spectra by computational modeling, both electronic and nuclear quantum effects must be included. We show that after reparameterization of the popular clay forcefield CLAYFF, the O-H stretching region of their vibrational spectra better matches the experimental one, with no detriment to the model's agreement with other experimental properties.
氢键在黏土化学中至关重要，它介导了黏土表面与水之间的相互作用，对于某些材料而言还介导了不同层之间的相互作用。众所周知，黏土计算模型的准确性取决于处理电子结构的理论水平。然而，对于氢键体系，轻氢原子核在电子势能面上的运动常常受到量子离域的影响。通过路径积分分子动力学，我们表明核量子效应导致黏土结构发生相对较小的变化，但这种变化与在不同电子结构理论水平下处理黏土所引起的变化相当。考虑量子效应会削弱黏土中的氢键，黏土不同层之间的氢键比同一层内的氢键受到的影响更大；这归因于氢原子在层内的受限状态与其参与氢键形成无关这一事实。更重要的是，核量子效应导致的氢键减弱会引起这些体系振动光谱的变化，显著地使O - H伸缩峰发生位移，这意味着为了通过计算建模全面理解这些光谱，必须同时考虑电子和核量子效应。我们表明，在对常用的黏土力场CLAYFF进行重新参数化之后，其振动光谱的O - H伸缩区域能更好地与实验结果匹配，且不会损害该模型与其他实验性质的一致性。
